Methods and devices for charring plant matter may be grouped into two broad categories: first, industrial ovens with a large production capacity, which are highly sophisticated and involve the mobilization of significant financial and human resources. In the second group are ovens based on the ancient kiln, which operate without any outside energy source. The latter are used in almost all small and medium production units. However, their operation involves a number of disadvantages, and they permit neither the processing of gases nor the recovery of tars.
Many of the problems associated with methods and devices discussed above have been overcome by the invention described. This invention relates to an oven for charring wood and plant matter of the "downdraft intermittent operation" type, not requiring any outside energy source. It includes a series of innovations that facilitate handling and permit exact adjustment and a high degree of reliability. It can be easily incorporated into a well-organized worksite, with excellent operating economy.
The apparatus includes a metal cylinder placed on four feet with a fireproof insulating layer, mechanically shielded, covering the entire inside wall. The circular upper cover, which is operated manually from the ground, permits loading and has a direct draft aperture, also operated from the ground. Within the oven above the bottom, a hearth composed of stationary metal plates is arranged for holding the wood. In this space a number of essential functions of the machine take place. Quick removal from the oven by simple gravity is facilitated. A central opening with a 60 cm diameter provides for the rapid fall of the charcoal. For this purpose a section of the hearth is provided with a removable cover.
The invention described herein also provides for the collection of gases, pyroligneous liquors, and tars. An annular space located around the central discharge opening provides for the collection of gases and other products coming from the interior of the oven and directs them toward the stack of the single flue.
Each exterior air intake consists of a pipe welded to the bottom of the oven. It can be closed by means of a metal disk applied by a center screwshaft, a wheel and a stationary clamp. Adjustment is therefore exact and tightness is assured at the end of the cycle. These intakes are arrranged at the periphery of the bottom of the oven. Each consists of a metal box covering the air intake pipe and includes two outlets punched with holes admitting fresh air into the oven above the hearth.
The hearth itself is made of plates reinforced by bending and punched with holes permitting the passage of gases from the oven into the space between the hearth and the bottom. Openings of variable height and width permit the access of these gases, liquors and tars into the annular space which directs them to the stack of the flue.
Because of the innovations described above, the oven works well in any small or medium facility, where it provides numerous advantages. It is easy to use and provides autonomous operation. The manner of sealing and operation provide a clean, dust-free workplace. The air flows can be controlled by exact, reliable adjustment. The oven is completely airtight at the end of the cycle and cools quickly. The charred material is of high quality with substantially no tars or toxic by-products. The oven is energy efficient since no external energy source is required. Collection of all by-products is readily achieved and the collected gases, tars can be treated by known methods. Certain condensers can be used without adaptation.
The above has been a brief discussion of some advantages of the invention and disadvantages of existing methods and apparatus. Additional advantages can be appreciated for the detailed description of the preferred embodiment which follows.